Type II and III archetypal strains predominate in Europe and usually show intermediate to low virulence in mice. Recently, short-term laboratory adaptation has been demonstrated in a set of 6 recently isolated canonical strains, where their phenotypic traits, in terms of parasite proliferation, cystogenesis and virulence in outbred mice, suffered from modifications after 40 passages in vitro (Colos-Arango et al., 2023). Aiming to investigating the molecular basis underlying such phenotypic changes, a comparative transcriptomic analysis of parasites harvested at low (10-15) and high (50-55) passage numbers, was carried out. Principal Component Analysis, showed that the transcriptional changes are mainly determined by the culture passage number and the clonal genetic type of the parasites. Passage conditions are presumably determined by specific genes related to protein synthesis, cytoskeleton and secretory pathogenesis. Enrichment analyses demonstrated that genes related to host-parasite interaction, protein synthesis, and metabolism-related mechanisms are overexpressed in Type II strains, while those related to gene expression regulation are predominant within Type III isolates. In addition, we found that genes involved in cyst formation and chronic infection in mice, were overexpressed at the low passage condition. Finally, Weighted Gene Co-expression Network Analysis was able to correlate phenotypic data obtained in vitro (e.g. tachyzoite yield and tachyzoite-to-bradyzoite conversion) and in vivo (e.g. morbidity and parasite loads in lung) with differential expression of gene modules. In conclusion, profound changes are observed in the transcriptomic profile after short term passage in vitro of recently obtained T. gondii isolates, warranting future experiments aimed at unraveling gene expression regulation (e.g., epigenetic) in these isolates.

Funded by Spanish Research Agency through the grant PID2022-138673OB-C21

Reference

Colos-Arango et al. (2023). Short-term culture adaptation of Toxoplasma gondii archetypal II and III field isolates affects cystogenic capabilities and modifies virulence in mice. International Journal for Parasitology, 53(9), 491–504.